CN105671447B - The excellent high yield of hole expandability is than type high strength cold rolled steel plate and its manufacture method - Google Patents
The excellent high yield of hole expandability is than type high strength cold rolled steel plate and its manufacture method Download PDFInfo
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- CN105671447B CN105671447B CN201510259439.0A CN201510259439A CN105671447B CN 105671447 B CN105671447 B CN 105671447B CN 201510259439 A CN201510259439 A CN 201510259439A CN 105671447 B CN105671447 B CN 105671447B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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Abstract
The present invention discloses a kind of excellent high yield of hole expandability than type high strength cold rolled steel plate and its manufacture method.The cold-rolled steel sheet, by weight % are counted, including：C:0.035~0.07%；Si:Less than 0.3% (except 0%)；Mn:2.0~3.5%；Cr:0.3~1.2%；Ti:0.03~0.08%；Nb:0.01~0.05%；Sol.Al:0.01~0.10%；B:0.0010~0.0050%；Surplus Fe and inevitable impurity, in terms of microstructure, based on area fraction, include the martensite of more than 90% (including 100%), the average grain diameter of the martensite is less than 3 μm, and the martensite includes tempered martensite and lath martensite, and the average grain diameter of the lath martensite is less than 1 μm, particle diameter in the lath martensite is that the area fraction of more than 1 μm of lath martensite is less than 5%, including 150/μm2A diameter of below 10nm above precipitate.
Description
Technical field
The present invention relates to a kind of excellent high yield of hole expandability than type high strength cold rolled steel plate and its manufacture method, in more detail
Ground, it is related to a kind of available for structural partsof automobiles such as component (member), seat crosspiece (seat rail), pillars (pillar)
The excellent high yield of hole expandability than type high strength cold rolled steel plate and its manufacture method.
Background technology
In recent years, with the reinforcing of various environmental legislations and energy supervision mechanism, in order to improve automobile fuel efficiency and resistance to
Long property is, it is necessary to the automotive sheet of high intensity.Particularly, with the propagation of vehicle impact safety codes, in order to improve car body
Impact resistance just widely using high-strength steel sheet as component (member), seat crosspiece (seat rail), pillar
(pillar) the structure member steel plate such as.This high-strength steel sheet is designed to absorb the impact energy of automobile, therefore,
It is characterized in that the yield strength of steel plate is higher than tensile strength, i.e. yield ratio (yield strength/tensile strength) is high.
On the other hand, Automobile frame as described above also passes through in addition to being manufactured by the method for roll forming
Stamping forming method manufacture, therefore the high-strength steel sheet needs have excellent hole expandability.But generally with steel plate
Intensity enhancing, reduction of pliability, so as to cause hole expandability to deteriorate, therefore need to research and develop the member that can improve this phenomenon at present
Part.
Related to this is carried out Patent Document 1 discloses a kind of in order to improve the yield strength of steel in continuous annealing
The technology of water cooling.That is, during annealing process, it is immersed in after steel plate is carried out into all heat-treated in water tank (water tank),
Temper is carried out, so as to manufacture the steel plate that microstructure is tempered martensite.But to the skill by the patent document 1
When the steel plate of art manufacture carries out water cooling, due to the temperature deviation on width and length direction, its shape quality is inferior, because
This, in the case of using the method for roll-forming, has that processing type reduces and material deviation according to position etc. is serious lacks
Point.
Also, Patent Document 2 discloses a kind of in order to improve the intensity and ductility of steel simultaneously, from microcosmic group of steel
From the point of view of knitting aspect, be formed as the technology of tempered martensite and ferritic complex tissue.But pass through the patent document 2
The steel plate of technology manufacture, because carbon addition is excessive, may result in that weldability is poor, and because the addition of silicon is excessive, may
Trigger and indenture is produced in stove.
Prior art literature
Patent document
1 Japanese granted patent gazette of patent document the 2528387th
The Japanese granted patent gazette JP 2010-90432 of patent document 2
The content of the invention
(1) technical problems to be solved
According to an aspect of the present invention, the purpose is to be made up of suitable control alloy and manufacturing condition, so as to provide
The excellent high yield of hole expandability is than type high strength cold rolled steel plate and its manufacture method.
(2) technical scheme
To achieve these goals, one aspect of the present invention, there is provided a kind of excellent high yield of hole expandability is more high-strength than type
Cold-rolled steel sheet is spent, % by weight is counted, including：C:0.035~0.07%, Si:Less than 0.3% (except 0 weight %), Mn:2.0~
3.5%th, Cr:0.3~1.2%, Ti:0.03~0.08%, Nb:0.01~0.05%, Sol.Al:0.01~0.10%, B:
0.0010~0.0050%, surplus Fe and inevitable impurity, in terms of microstructure, based on area fraction, bag
The martensite of more than 90% (including 100%) is included, the average grain diameter of the martensite (martensite) is less than 3 μm, described
Martensite includes tempered martensite (tempered martensite) and lath martensite (lath martensite), the plate
The average grain diameter of bar martensite is less than 1 μm, the area for the lath martensite that the particle diameter in the lath martensite is more than 1 μm
Fraction is less than 5%, including 150/μm2A diameter of below 10nm above precipitate.
Also, another aspect of the present invention, there is provided a kind of excellent high yield of hole expandability is than type high strength cold rolled steel plate
Manufacture method, comprise the following steps：Steel billet is reheated, wherein, the steel billet is in terms of weight %, including C:0.035~
0.07%th, Si:Less than 0.3% (except 0 weight %), Mn:2.0~3.5%, Cr:0.3~1.2%, Ti:0.03~0.08%,
Nb:0.01~0.05%, Sol.Al:0.01~0.10%, B:0.0010~0.0050%, surplus Fe and inevitably it is miscellaneous
Matter；Hot rolling is carried out to obtain hot rolled steel plate to the steel billet of the reheating；Batch the hot rolled steel plate；The hot rolling to batching
Steel plate carries out cold rolling, to obtain cold-rolled steel sheet；In 780~850 DEG C, continuous annealing treatment is carried out to the cold-rolled steel sheet；With 1
~10 DEG C/sec speed, the cold-rolled steel sheet for carrying out continuous annealing treatment is once cooled to 650~700 DEG C；With 5~20
DEG C/sec speed, then the cold-rolled steel sheet secondary cooling once cooled down to (Ms-100)~Ms DEG C was carried out
Ageing Treatment.
The feature of the present invention all is not enumerated out in addition, above-mentioned technical problem solves method.Pass through
Following embodiment, the various technical characteristics of the present invention can be understood in further detail and the advantages of based on this feature and
Effect.
(3) beneficial effect
According to the present invention it is possible to provide, a kind of material deviation is small, and yield ratio and the excellent high intensity cold steel rolling of hole expandability
Plate.
Brief description of the drawings
Fig. 1 is the figure for the microstructure for observing example 6.
Fig. 2 is the figure of the precipitate in the steel for observe example 6.
Embodiment
It is well known that typically in order to improve the yield ratio of steel plate and hole expandability, it is to be ensured that cryo tissue.Therefore, with low temperature
The martensite with maximum intensity in tissue receives much concern always for the steel plate of Main Tissues.As described above, in order to formed with
Martensitic structure is the steel plate of Main Tissues, and method the most common is that the sufficiently long time is kept when being made annealing treatment, with
Just austenite can be formed, (water cooling) is then quickly cooled down and carries out temper.But as it was previously stated, this method meeting
The problems such as causing material deviation and unqualified shape.
Therefore, the present inventor is by the species and content of suitable control alloying element, so as to attempt to ensure that geneva
Body.More specifically, largely addition manganese and chromium etc. improves the element of quenching degree, to can also ensure that horse in low cooling velocity
Family name's body.On the other hand, in this case, weldability deterioration, the increase of hot rolling intensity etc. are produced because largely adding alloying element
Problem, therefore the present inventor wants to reduce the carbon content for producing weldability maximum effect to greatest extent.
But alloy design result as described above, due to the carbon content deficiency in martensite so that can not fully strengthen
Yield strength, therefore generate the problem of yield ratio reduces.Therefore, in order to solve described problem, the present inventor is carried out
In-depth study, as a result knows by being properly added carbide, nitride forming element, and suitable control manufacturing condition,
So as to while carbide, nitride are uniformly distributed in microstructure, by refining martensitic crystal grains size, can carry simultaneously
The yield ratio and hole expandability of high steel plate, and complete the present invention.
Below, the high yield excellent to the hole expandability of one aspect of the present invention is carried out in detail than type cold-rolled steel sheet
It is bright.
Carbon (C)：0.035~0.07 weight %
The element that carbon is for ensuring that the intensity of steel and added.Also, in the structural transformation of cold-rolled steel sheet such as of the invention
Steel in, play the formation for promoting martensite, and increase the effect of the fraction of the martensite in steel.In order to obtain such effect
Fruit, in the present invention, it is preferred to, including more than 0.035% weight %, it is highly preferred that including more than 0.038 weight %, then more
Preferably, including more than 0.040 weight %.On the contrary, when carbon content is excessive, the intensity of martensite is too high so that with carbon content phase
It is such as excessive with ferritic strength difference to the second low phase, apply stress to it in the case, hold between two-phase on interface
Crack is also easy to produce, therefore, reduces the stretch flangeability of steel.Also, because weldability deteriorates, there may be weld defect during processing.
Therefore, the higher limit of the carbon content is preferably 0.07 weight %, more preferably 0.068 weight %, still more preferably from 0.065 weight
Measure %.
Silicon (Si)：Below 0.3 weight % is (except 0%)
Silicon is the element for promoting ferritic transformation, therefore silicon can't be intentionally added in the present invention.Also, the silicone content
When excessive, the carbon content in the austenite not changed can be increased, reduce the intensity of martensite, the microstructure of steel is formed as iron
The complex tissue of ferritic and martensite.Also, exist and trigger surface scale defect, reduce the surface quality of steel plate, and drop
The problem of low chemical treatment properties.It is therefore preferred that silicone content is controlled as far as possible minimum, the higher limit of the silicone content is excellent
Elect 0.3 weight %, more preferably 0.2 weight % as.
Manganese (Mn)：2.0~3.5 weight %
Manganese is by crystal grain thinning, and the S in steel is separated out with MnS completely, is prevented so as to have based on the hot-short of generation FeS
Property, meanwhile, pass through the effect of solution strengthening reinforcing steel in the case where not reducing ductility.Also, reduce and turn for martensite
The critical cooling rate of change, more easily to ensure martensitic structure.In order to obtain such effect, included in the present invention
Manganese content is preferably more than 2.0 weight %, more preferably more than 2.2 weight %, then more preferably more than 2.4 weight %.So
And manganese content it is excessive when, weldability and hot rolling may be reduced.Therefore, the higher limit of the manganese content is preferably 3.5 weights
Measure %, more preferably 3.2 weight %, then more preferably 3.1 weight %.
Chromium (Cr)：0.3~1.2 weight %
Chromium not only improves the intensity of steel, but also improves the quenching degree of steel, therefore is to form the martensite of low-temperature transformation
The element to be played an important role in terms of phase transformation.In order to obtain such effect, the chromium content included in the present invention is preferably 0.3 weight
More than % is measured, more preferably more than 0.4 weight %, then more preferably more than 0.5 weight %.However, when chromium content is excessive, because
Excessively strengthen hot rolling intensity, the problem of cold-rolling property deterioration be present.Therefore, the higher limit of the chromium content is preferably 1.2 weight %,
More preferably 1.1 weight %.
Titanium (Ti)：0.03~0.08 weight %
Titanium not only improves the intensity of steel, and is combined with the carbon in steel and/or nitrogen, forms fine silicon carbide thing, nitride, from
And played an important role in terms of crystal grain thinning.On the other hand, fine silicon carbide thing as described above, nitride strengthening matrix group
Knit, and reduce the hardness ratio between two-phase, so as to be played an important role in terms of the yield strength of steel and stretch flangeability is improved.
In order to obtain such effect, the Ti content included in the present invention is preferably more than 0.03 weight % more preferably 0.035 weight
More than % is measured, then more preferably more than 0.04 weight %.On the contrary, when Ti content is excessive, economy is not only reduced, and because of shape
Into excessive carbide, nitride, the ductility of steel may be greatly reduced.Therefore, the higher limit of the Ti content is preferably
0.08 weight %, more preferably 0.065 weight %, then more preferably 0.055 weight %.
Niobium (Nb)：0.01~0.05 weight %
Niobium not only improves the intensity of steel, and is combined with the carbon in steel and/or nitrogen, forms fine silicon carbide thing, nitride, from
And played an important role in terms of crystal grain thinning.On the other hand, fine silicon carbide thing as described above, nitride strengthening matrix group
Knit, and reduce the hardness ratio between two-phase, so as to be played an important role in terms of the yield strength of steel and stretch flangeability is improved.
In order to obtain such effect, the content of niobium included in the present invention is preferably more than 0.01 weight % more preferably 0.02 weight
More than % is measured, then more preferably more than 0.03 weight %.On the contrary, when content of niobium is excessive, economy is not only reduced, and because of shape
Into excessive carbide, nitride, the ductility of steel may be greatly reduced.Therefore, the higher limit of the content of niobium is preferably
0.05 weight %, more preferably 0.04 weight %, then more preferably 0.035 weight %.
Soluble aluminum (Sol.Al)：0.01~0.10 weight %
Soluble aluminum (Al) is used as strong deoxidier, can reduce the oxygen content in molten steel, is effective element when manufacturing clean steel.
Also, combined with the nitrogen in steel and separate out AlN, so as to have the function that to reduce solid solution nitrogen.In order to obtain such effect, the present invention
In the solvable aluminium content that includes be preferably more than 0.01 weight %, more preferably more than 0.015 weight %, then be more preferably
More than 0.02 weight %.However, when solvable aluminium content is excessive, not only increase production cost, and because separating out excessive AlN, increase
The danger that slab slight crack is produced during impact is added.Therefore, the higher limit of the solvable aluminium content is preferably 0.10 weight %, more excellent
Elect 0.08 weight %, then more preferably 0.05 weight % as.
Boron (B)：0.0010~0.0050 weight %
During being cooled down after continuous handling return is carried out to cold-rolled steel sheet, boron not only postpones austenite to pearly-lustre
The transformation of body, and suppress ferritic formation, promote the formation of martensite.In order to obtain such effect, wrapped in the present invention
The Boron contents contained are preferably more than 0.0010 weight %, more preferably more than 0.0015 weight %, then more preferably 0.0018
More than weight %.However, when Boron contents are excessive, because forming excessive ferroalloy, cause to increase unnecessary cost.Therefore, institute
The higher limit for stating Boron contents is preferably 0.0050 weight %, more preferably 0.0040 weight %, then more preferably 0.0030 weight
Measure %.
In addition to mentioned component, remaining is iron (Fe).Simply, generally in the fabrication process, will necessarily be from raw material and week
Surrounding environment is mixed into unexpected impurity, therefore can not exclude these impurity.Those skilled in the art can know this
A little impurity, therefore do not illustrate in this manual.
However, phosphorus therein, sulphur and nitrogen are the general impurity often referred to, will be briefly explained below.
Phosphorus (P)：Below 0.10 weight % (except 0 weight %)
Phosphorus be inevitably by containing impurity, be element the main reason for segregating to crystal boundary and reduce ductility,
It is therefore preferred that phosphorus content is controlled minimum as far as possible.Preferably the content of phosphorus is controlled in 0 weight % in theory, but
In manufacturing process necessarily by containing.Accordingly manage the higher limit of phosphorus content.The upper limit of the phosphorus content in the present invention
Value is preferably 0.10 weight %, more preferably 0.05 weight %, then more preferably 0.03 weight %.
Sulphur (S)：Below 0.010 weight % (except 0 weight %)
Sulphur be inevitably by containing impurity, be reduce steel ductility and weldability the main reason for element,
It is therefore preferred that sulfur content is controlled minimum as far as possible.Preferably the content of sulphur is controlled in 0 weight % in theory, but
In manufacturing process necessarily by containing.Accordingly manage the higher limit of sulfur content.The upper limit of the sulfur content in the present invention
Value is preferably 0.01 weight %, more preferably 0.005 weight %.
Nitrogen (N)：Below 0.01 weight % (except 0 weight %)
Although beneficial effect of the nitrogen with stable austenite in steel, by forming AlN etc., increase produces when impacting
The danger of slight crack, therefore, it will not intentionally add in the present invention.It is therefore preferred that nitrogen content is controlled as far as possible minimum,
The higher limit of the nitrogen content is preferably 0.01 weight %, more preferably 0.008 weight %, then more preferably 0.007 weight
Measure %.
Below, the preferred microstructure and precipitate of cold-rolled steel sheet of the invention are described in detail.
Preferably, cold-rolled steel sheet of the invention meets the condition of above-mentioned constituent, meanwhile, in terms of area fraction, its is micro-
Sight is organized as the martensite for including more than 90% (including 100%).Now, the martensite includes tempered martensite and lath horse
Family name's body.On the other hand, in addition to the martensite, its impure tissue may include ferrite (ferrite), bainite (bainite)
With granular bainite (granular bainite), the area fraction sum of these tissues is preferably less than 10% (including 0%).
Also, the average grain diameter of the martensite is preferably 3 μm, the average grain diameter of the lath martensite is preferably 1 μm,
The area fraction for the lath martensite that particle diameter in the lath martensite is more than 1 μm is preferably less than 5%.It is although of the invention
Cold-rolled steel sheet steel in carbon content it is very low, be unfavorable for ensuring hardness, still, as described above, control martensitic crystal grains it is big
It is small, make its scaled fine, so as to ensure excellent yield ratio.Now, particle diameter refers to observe the section of steel plate and detect
Martensite equivalent diameter (equivalent circular diameter).
Preferably, cold-rolled steel sheet of the invention includes 150/μm2A diameter of below 10nm above precipitate.
This, precipitate refers to the compound carbonitride of titanium carbonitride, niobium carbonitrides or titanium, niobium.By will finely separate out as described above
Thing is evenly distributed in microstructure, so as to suitable control martensite hardness raising and two alternate hardness ratios, by
This is able to ensure that excellent hole expandability.
According to the specific embodiment of the present invention, the hardness of the martensite can be more than 350Hv, the cold-rolled steel
Two alternate hardness ratios of plate can be less than 1.5.Described two alternate hardness ratios refer to that having in microstructure is minimum hard
The hardness of the tissue of degree and the ratio for having the hardness of glass-hard tissue.Now, the hardness of the microstructure can profit
With nano impress (nano-indenter, NT110) instrument, by measuring 3 100point under 2g load with square,
Then calculate the average value for the remaining measured value for removing maximum and minimum value and obtain.
According to the specific embodiment of the present invention, the cold-rolled steel sheet of the present invention as described above can have more than 600MPa
Yield strength, more than 0.8 yield ratio and more than 50% hole expandability (HER, Hole Expansion Ratio), thus
Preferably suitable for the structural partsof automobiles such as component, seat crosspiece, pillar.
Above-mentioned cold-rolled steel sheet of the invention can be manufactured by various methods, be not particularly limited its manufacture method.Only
It is that one of specific embodiment can be manufactured by following method.
Below, the manufacturer of the yield-ratio high-strength cold-rolled steel sheet excellent to the hole expandability of another aspect of the present invention
Method is described in detail.
First, the steel billet with above-mentioned composition is reheated, then carries out hot rolling to obtain hot rolled steel plate.Carry out heat
Before rolling, although the temperature conditionss in the step of being reheated to steel billet are not particularly limited, it is preferred that using common
Relation reheating temperature is reheated.
According to the specific embodiment of the present invention, when carrying out the hot rolling treatment, the temperature of finish to gauge outlet side can be
870~950 DEG C, it is preferable that can be 880~920 DEG C.When the temperature of finish to gauge outlet side is less than 870 DEG C, thermal deformation can be caused
The possibility that impedance sharply increases becomes big, and the top (top) of hot rolling coil and afterbody (tail) and edge turn into single-phase
Area, may make the anisotropy increase in plane and mouldability deteriorates.On the contrary, when the temperature of finish to gauge outlet side is more than 950 DEG C
When, blocked up oxide skin is not only produced, and may be roughened the microstructure of steel plate.
Then, the hot rolled steel plate is batched.According to the specific embodiment of the present invention, coiling temperature can be 600~
750 DEG C, it is preferable that can be 650~720 DEG C.When coiling temperature is less than 600 DEG C, excessive martensite or bainite are generated,
The hardness of hot rolled steel plate is caused excessively to improve, because load causes asking for the manufacture views such as shape defect during so as to which cold rolling occurs
Topic.On the contrary, when coiling temperature is more than 750 DEG C, it because of the increase of surface scale, may deteriorate pickling.
Then, pickling processes are carried out to the hot rolled steel plate batched, then carries out cold rolling to obtain cold-rolled steel sheet.According to this hair
A bright specific embodiment, the reduction ratio during cold rolling can be 40~70%, it is preferable that can be 45~55%.When
When reduction ratio is less than 40%, recrystallization driving force reduces, and can make problem occurs during the good recrystallization grain of acquisition, and correct shape
It is extremely difficult.On the contrary, when reduction ratio is more than 70%, not only increase sharply rolling load, and may be in edges of plate
(edge) portion produces crack (crack).
Then, continuous annealing treatment is carried out to the cold-rolled steel sheet.Now, annealing temperature as cooling termination temperature (after
The cooling termination temperature once, after secondary cooling stated), be an important factor for being managed in the present invention in one.In order to
Ensuring more than 0.80 yield ratio (YR) and more than 50% HER proposed in the present invention, the annealing temperature is preferably 780~
850 DEG C, more preferably 800~830 DEG C.When annealing temperature is less than 780 DEG C, substantial amounts of ferrite is formed, so as to reduce surrender
Than, and two alternate hardness have the problem of reducing hole expandability than increase.On the contrary, when annealing temperature is more than 850 DEG C,
Because of the roughening of the austenite crystal based on high annealing so that by cooling described later and the martensite packets of acquisition
(packet) size increases, and has the problem of can not ensuring less than 3 μm of the fine martensitic structure proposed in the present invention.
Then, the cold-rolled steel sheet of the progress continuous annealing treatment is once cooled down.Cooling stage is
For suppressing ferritic transformation, it is ensured that the step of martensitic structure is the Main Tissues of steel plate.
Now, a cooling velocity is preferably 1~10 DEG C/sec, more preferably 1~5 DEG C/sec.Once cooled down when described
When speed is less than 1 DEG C/sec, ferritic transformation is partly produced in cooling procedure, reduce yield ratio, and two is alternate hard
Degree has the problem of hole expandability reduces than increase.On the contrary, when a cooling velocity is more than 10 DEG C/sec, has and pass through
The problem of being bent during coil.
Also, a cooling termination temperature is preferably 650~700 DEG C, more preferably 650~680 DEG C.When described once cold
But when final temperature is less than 650 DEG C, coil bending may be made, when a cooling termination temperature is more than 700 DEG C, because cold
But speed reduces, and may produce the problems such as yield ratio based on ferritic formation reduces.
Then, secondary cooling is carried out to the cold-rolled steel sheet once cooled down.This step is by quickly cooling down so that
The austenite ensured in continuous annealing process is transformed into martensite, so as to be for the area fraction for ensuring to propose in the present invention
The step of more than 90% martensite.
Now, secondary cooling speed is preferably 5~20 DEG C/sec.When the secondary cooling speed is less than 5 DEG C/sec, deposit
When martensite transfor mation can not be obtained the problem of required sufficient cooling performance.On the contrary, when the secondary cooling speed is more than
During 20 DEG C/sec, the quality problems such as coil shape distortion caused by quick cooling can be produced.
Also, secondary cooling final temperature preferably (Ms-100)~Ms DEG C, more preferably (Ms-50)~Ms DEG C.It is described
Secondary cooling final temperature is for ensuring that high yield ratio and high as ensured the width of coil and the shape of length direction
The very important temperature conditionss of hole expandability, when the secondary cooling final temperature is less than (Ms-100) DEG C, at overaging
The excessive increase of martensite during reason so that yield ratio and tensile strength excessively increase, so as to asking with reduction ductility
Topic.On the contrary, when the secondary cooling final temperature is more than Ms DEG C, the austenite generated during annealing is not changed into martensite,
But the bainite of generation high-temperature phase-change, granular bainite (granular bainite) etc., so as to have yield strength drastically
The problem of deterioration.The tissue not only deteriorates yield ratio, but also along with hole expandability deterioration the problem of.As reference, Ms
Value is calculated by following mathematical expression 3.
[mathematical expression 3]
Ms (DEG C)=561-474 (wt%C) -33 (wt%Mn) -17 (wt%Cr) -17 (wt%Ni) -21 (wt%Mo)
Wherein, wt% represents the content (weight %) of respective element respectively.
Then, after completing the secondary cooling, Wetted constructures are carried out under the secondary cooling final temperature.According to this
One specific embodiment of invention, the Wetted constructures time can be 100~800 seconds, preferably 200~600 seconds.When the mistake
When aging time is less than 100 seconds, sufficient temper cannot get and the martensite generated by the secondary cooling, because
This, may obtain excessive lath martensite tissue.On the contrary, when being more than 800 seconds the Wetted constructures time, although energy
Enough ensure expected microstructure, but may be because of excessive temper so that hardness reduces.
According to the specific embodiment of the present invention, after the Wetted constructures, can also include with 0.1~10% pressure
Lower rate carrys out the step of smooth (skin pass) rolling.Generally, during the steel of skin pass rolling transformation tissue, will not largely increase anti-
Zhang Qiangdu, and improve 50 to more than 100MPa yield strength.Now, when reduction ratio is less than 0.1%, such as superelevation of the present invention
Shape is difficult to control in strength steel, on the contrary, when being processed in the case that reduction ratio is more than 1.0%, yield strength excessively increases
Add.Also, operated by high elongation, operability can be made to become very unstable, therefore, reduction ratio during skin pass rolling is preferably
0.1~1.0%.
Below, it is described in more details by embodiments of the invention.But these embodiments are only intended to illustrate
The implementation of the present invention, the present invention are not limited to this.Because protection scope of the present invention is by remembering in claims
The item of load and the item that thus rationally derives and determine.
Embodiment
Vacuum melting is carried out to the steel billet of such as table 1 below composition, carries out one under 1200 DEG C of heating-up temperature in heating furnace
The reheating of individual hour, then condition in table 2 below carry out hot rolling and batch.Then, the hot rolled steel plate that pickling is batched, with
45% reduction ratio carries out cold rolling, is derived from cold-rolled steel sheet, then the condition in table 2 below carry out continuous annealing treatment,
Once cooling and secondary cooling.Afterwards, 300 seconds Wetted constructures are carried out under secondary cooling final temperature.Now, make once
Cooling velocity perseverance is 2 DEG C/sec, and a permanent cooling termination temperature is 650 DEG C, and secondary cooling speed perseverance is 15 DEG C/sec.
Then, phase fraction, size and the hardness of the microstructure of each manufactured cold-rolled steel sheet of measurement, and checked analysis
Go out the size and distribution density of thing, its result is included in table 3.Also, JIS5 tensile strength test pieces are made, measurement is bent
Intensity (YS), tensile strength (TS), yield ratio (YR=YS/TS), elongation (T-El) and hole expandability are taken, and its result is shown
Show in table 4.
Now, the size and distribution density of the phase fraction of the microstructure and size and precipitate are seen by FE-TEM
Examine, then measured using graphical analysis (image analyzer) equipment.Also, the hardness of the microstructure is profit
With nano impress (NT110) instrument, by measuring 3 100point under 2g load with square, then calculate and remove most
The average value of the remaining measured value of big value and minimum value and obtain.
[table 1]
[table 2]
[table 3]
[table 4]
As shown in Table 3 and Table 4, the geneva bulk area of the composition range of the present invention and the example 1 to 9 of manufacturing condition is met
Fraction is shown as minimum more than 94%, and martensite average grain diameter is less than 1.7 μm.Also, the lath martensite in the presence of steel
Size be shown as less than 0.9 μm, while particle diameter is that the fraction of more than 1 μm of lath martensite is shown as within 2 area %.And
And the average hardness value of martensite is shown as minimum more than 350Hv, two alternate hardness ratios be also displayed as being up to 1.4 with
Under.On the other hand, a diameter of below 10nm precipitate meets 150/μm proposed in the present invention2More than.Therefore, invent
The yield ratio of example 1 to 9 is that more than 0.8, HER is more than 50%, it can thus be appreciated that it has excellent yield ratio and hole expandability.
Fig. 1 is the figure for the microstructure for observing example 6.As shown in Figure 1, less than 1 μm of fine lath horse be present
Family name's body.Fig. 2 is the figure of the precipitate in the steel for observe example 6.It can confirm that the fine analysis that distributed substantial amounts of below 10nm
Go out thing.
Although the alloy composition of comparative example 1 and 2 meets scope proposed by the present invention, secondary cold in manufacturing condition
But final temperature generates bainite and granular bainite of high-temperature phase-change etc., therefore beyond scope proposed by the invention
The hardness of martensite reduces, and two alternate hardness are than increase, so that its yield ratio reduces, hole expandability deterioration.
The annealing temperature of comparative example 3 is not reaching to scope proposed by the invention, but is annealed in out-phase region
Processing, therefore, forms substantial amounts of ferrite, so as to reduce yield ratio, and adds two alternate hardness ratios so that it expands
Permeability deteriorates.
The annealing temperature of comparative example 4 is beyond scope proposed by the invention, because of the austenite crystal based on high annealing
Roughening so that martensite packets size increases, so as to ensure less than 3 μm of martensitic structure being proposed in the present invention
With less than 1 μm of lath martensite tissue so that its yield ratio reduce, the deterioration of hole expandability.
Carbon content in comparative example 5 to 8 is beyond the scope proposed in the present invention.Which results in the cooling after annealing
The increased result of the hardness of caused lath martensite in step.But lath martensite as described above is highly stable
Phase, intactly remaining it can also get off even if by Wetted constructures, by Wetted constructures and the tempered martensite that generates
The situation of body, because the precipitation of carbon can reduce hardness, therefore two alternate hardness, so that its yield ratio reduces, expand than increase
Permeability deteriorates.
The manganese content of comparative example 9 is not reaching to the scope proposed in the present invention, can not substantially ensure that the Line Integral of martensite
Count, the chromium content in comparative example 10 and 11 is not reaching to the scope proposed in the present invention, therefore forms thick martensite.By
This so that its yield ratio reduces, hole expandability deterioration.
Silicone content in comparative example 12 forms substantial amounts of ferrite, so as to nothing beyond the scope proposed in the present invention
Method ensures sufficiently martensitic area fraction, and as a result the hardness of martensite reduces, two alternate hardness ratio increases, so that its
Yield ratio reduces, hole expandability deterioration.
Ti content and content of niobium in comparative example 13 are not reaching to the scope proposed in the present invention.In the titanium and niobium and steel
Carbon combine, formed carbide, this carbide have strengthen matrix, and reduce by two alternate hardness than effect.But
It is that Ti content in comparative example 13 and content of niobium are less, sufficient precipitate can not be formed, therefore cause the reduction of its yield ratio, expands
Permeability deteriorates.
Claims (12)
1. a kind of excellent high yield of hole expandability is counted than type high strength cold rolled steel plate, by weight %, including：C:0.035~
0.07%；Si:Less than 0.3%, except 0%；Mn:2.2~3.5%；Cr:0.4~1.2%；Ti:0.03~0.08%；Nb:
0.01~0.05%；Sol.Al:0.01~0.10%；B:0.0010~0.0050%；Surplus Fe and inevitable impurity,
In terms of microstructure, based on area fraction, include more than 90% martensite, described more than 90% includes
100%, the average grain diameter of the martensite is less than 3 μm,
The martensite includes tempered martensite and lath martensite,
The average grain diameter of the lath martensite is less than 1 μm, the lath horse that the particle diameter in the lath martensite is more than 1 μm
The area fraction of family name's body is less than 5%,
Including 150/μm2A diameter of below 10nm above precipitate.
2. the excellent high yield of hole expandability according to claim 1 is than type high strength cold rolled steel plate, it is characterised in that described
The microstructure of cold-rolled steel sheet also includes ferrite, bainite and granular bainite, and the area fraction sum of these tissues is
Less than 10%, except 0%.
3. the excellent high yield of hole expandability according to claim 1 is than type high strength cold rolled steel plate, it is characterised in that described
The hardness of martensite is more than 350Hv.
4. the excellent high yield of hole expandability according to claim 1 is than type high strength cold rolled steel plate, it is characterised in that described
Two alternate hardness ratios of cold-rolled steel sheet are less than 1.5.
5. the excellent high yield of hole expandability according to claim 1 is than type high strength cold rolled steel plate, it is characterised in that with weight
% meters are measured, the cold-rolled steel sheet also includes：P：Less than 0.10%, except 0%；S：Less than 0.010%, except 0%；And N：
Less than 0.010%, except 0%.
6. a kind of excellent high yield of hole expandability comprises the following steps than the manufacture method of type high strength cold rolled steel plate：
Steel billet is reheated, wherein, the steel billet is in terms of weight %, including C:0.035~0.07%；Si:0.3% with
Under, except 0%；Mn:2.2~3.5%；Cr:0.4~1.2%；Ti:0.03~0.08%；Nb:0.01~0.05%；
Sol.Al:0.01~0.10%；B:0.0010~0.0050%；Surplus Fe and inevitable impurity；
Hot rolling is carried out to obtain hot rolled steel plate to the steel billet of the reheating；
Batch the hot rolled steel plate；
Cold rolling is carried out to the hot rolled steel plate batched, to obtain cold-rolled steel sheet；
At 780~850 DEG C, continuous annealing treatment is carried out to the cold-rolled steel sheet；
With 1~10 DEG C/sec speed, the cold-rolled steel sheet for carrying out continuous annealing treatment is once cooled to 650~700 DEG C；
And
With 5~20 DEG C/sec speed, by the cold-rolled steel sheet secondary cooling once cooled down to (Ms-100)~Ms DEG C,
Then Wetted constructures are carried out.
7. for the excellent high yield of hole expandability according to claim 6 than the manufacture method of type high strength cold rolled steel plate, it is special
Sign is, the temperature of finish to gauge outlet side is 870~950 DEG C during the hot rolling.
8. for the excellent high yield of hole expandability according to claim 6 than the manufacture method of type high strength cold rolled steel plate, it is special
Sign is, described when batching, and coiling temperature is 600~750 DEG C.
9. for the excellent high yield of hole expandability according to claim 6 than the manufacture method of type high strength cold rolled steel plate, it is special
Sign is, during the cold rolling, reduction ratio is 40~70%.
10. for the excellent high yield of hole expandability according to claim 6 than the manufacture method of type high strength cold rolled steel plate, it is special
Sign is, when carrying out the Wetted constructures, the Wetted constructures time is 100~800 seconds.
11. for the excellent high yield of hole expandability according to claim 6 than the manufacture method of type high strength cold rolled steel plate, it is special
Sign is, after the Wetted constructures, in addition to 0.1~1.0% reduction ratio skin pass rolling the step of.
12. for the excellent high yield of hole expandability according to claim 6 than the manufacture method of type high strength cold rolled steel plate, it is special
Sign is, in terms of weight %, the cold-rolled steel sheet also includes：P：Less than 0.10%, except 0%；S：Less than 0.010%, 0% removes
Outside；And N：Less than 0.010%, except 0%.
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| KR1020140174085A KR101630975B1 (en) | 2014-12-05 | 2014-12-05 | High strength cold rolled steel sheet having high yield ratio and excellent hole expansibility and method for manufacturing the same |
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| KR101889181B1 (en) | 2016-12-19 | 2018-08-16 | 주식회사 포스코 | High-strength steel having excellent bendability and stretch-flangeability and method for manufacturing same |
| KR101917452B1 (en) | 2016-12-22 | 2018-11-09 | 주식회사 포스코 | Cold rolled steel sheet with excellent bendability and hole expansion property, and method for manufacturing the same |
| WO2018134186A1 (en) * | 2017-01-20 | 2018-07-26 | thyssenkrupp Hohenlimburg GmbH | Hot-rolled flat steel product consisting of a complex-phase steel having a predominantly bainitic microstructure and method for producing such a flat steel product |
| TWI616540B (en) * | 2017-01-26 | 2018-03-01 | Nippon Steel & Sumitomo Metal Corp | Steel plate |
| TWI627290B (en) * | 2017-02-02 | 2018-06-21 | Nippon Steel & Sumitomo Metal Corp | Steel plate |
| KR102020407B1 (en) * | 2017-12-21 | 2019-09-10 | 주식회사 포스코 | High-strength steel sheet having high yield ratio and method for manufacturing thereof |
| KR102075216B1 (en) * | 2017-12-24 | 2020-02-07 | 주식회사 포스코 | High strength steel sheet having high yield ratio and method for manufacturing the same |
| KR102075222B1 (en) * | 2017-12-26 | 2020-02-07 | 주식회사 포스코 | High strength cold rolled steel sheet having low mechanical properties deviation, good stretch flangeability and high recovery rate |
| JP6626918B2 (en) * | 2018-03-30 | 2019-12-25 | Ntn株式会社 | Bearing parts |
| CN108486462B (en) * | 2018-03-31 | 2019-10-25 | 唐山钢铁集团有限责任公司 | Reaming and the excellent high-yield-ratio cold-rolled steel sheet and its production method of bending property |
| JP2020012173A (en) * | 2018-07-20 | 2020-01-23 | 日本製鉄株式会社 | Steel material |
| CN108950405B (en) * | 2018-08-14 | 2020-02-18 | 武汉钢铁有限公司 | 800 MPa-grade multi-phase steel with good flanging performance and production method thereof |
| KR102487306B1 (en) * | 2020-12-21 | 2023-01-13 | 현대제철 주식회사 | Ultra high strength cold rolled steel sheet having excellent spot weldability and formability, ultra high strength galvanized steel sheet and method of manufacturing the same |
| WO2023223078A1 (en) * | 2022-05-19 | 2023-11-23 | Arcelormittal | A martensitic steel sheet and a method of manunfacturing thereof |
| CN116043109B (en) * | 2022-12-20 | 2024-05-14 | 攀钢集团攀枝花钢铁研究院有限公司 | Low-cost high-reaming-performance 980 MPa-grade hot-dip galvanized dual-phase steel and preparation method thereof |
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